Combustion flash bulb

ABSTRACT

A combustion flash bulb ignited by means of a piezo-electric ignition in which, to protect the wall of the envelope, a separate tubular inner envelope is arranged in the envelope, said inner envelope being open at its end facing the lamp base and comprising the metal wool to be burned. In order to attenuate the shock wave occurring during the combustion in the inner envelope, said inner envelope comprises opposite to the open tube end a narrowed end in which an aperture is provided. The inner envelope is thin-walled and manufactured from a soft glass.

United States Patent Boekkooi et al.

COMBUSTION FLASH BULB Inventors: Anton Boekkooi; Adrianus Antonius Hurx,both of Eindhoven; Johannes Cornelis van der Tas, Terneusen; CharlesCornelis Edward Meulemans, Eindhoven, all of Netherlands Assignee: U.S.Philips Corporation, New

York, N.Y.

Filed: Nov. 2, 1971 Appl. No.: 194,888

Foreign Application Priority Data Nov. 5. 1970 Netherlands ..70l6l82U.S. Cl ..431/95 Int. Cl ....F2lk 5/02 Field of Search ..43 1/93-95 [56]References Cited UNITED STATES PATENTS 2,865,l86 12/1958 Anderson et al...43l/93 Primary ExaminerCarroll B. Dority, Jr. Att0rneyFrank R. TrifariABSTRACT A combustion flash bulb ignited by means of a piezoelectricignition in which, to protect the wall of the envelope, a separatetubular inner envelope is arranged in the envelope, said inner envelopebeing open at its end facing the lamp base and comprising the metal woolto be burned. In order to attenuate the shock wave occurring during thecombustion in the inner envelope, said inner envelope comprises oppositeto the open tube end a narrowed end in which an aperture is provided.The inner envelope is thin-walled and manufactured from a soft glass.

5 Clainis, 1 Drawing Figure COMBUSTION FLASH BULB The invention relatesto a combustion flash bulb which comprises a hermetically sealedlight-pervious outer envelope and a tubular inner envelope which is openat its end facing the lamp base, the space in the inner envelopecommunicating with the space in the outer envelope, a filling of anoxidizable metal and an ignition mechanism being present in the innerenvelope, an oxygen-containing atmosphere prevailing inside the outerenvelope. Such a combustion flash bulb is known.

In the known flash bulb an inner envelope of a vitreous material is usedthe coefficient of expansion of which is very low, for example, Vycor orPyrex. By using such an inner tube of hard glass in which the ignitionmechanism is present, it is avoided that red-hot particles which duringthe explosive combustion of the ignition mass which forms part of theignition mechanism of the lamp are thrown away towards the inner wall ofthe outer envelope. On said wall of the outer envelope, such particlesmay give rise to the formation of shrinkage cracks as a result of whichsaid outer envelope is considerably weakened. By using an inner envelopewhich intercepts said particles and consists of a material having a verylow coefficient of expansion and which inner envelope will not breakduring firing the lamp, a protective layer of laquer which usuallycovers the outer envelope may in principle be omitted.

In the known combustion flash bulb a tubular inner envelope is usedwhich is open at one end and is closed in the form of a dome at itsother end which is present near the tipped-off end of the lamp. lthasnow been found that this construction exhibits a few drawbacks. First ofall, during evacuating the lamp and filling it with oxygen a rather longevacuating and transporting paths, respectively, is introduced which isformed by the non-tipped-off end of the exhaust tube at the end of thelamp, the narrow space between the side walls of the inner and the outerenvelope and the whole space of the inner envelope. This results in alonger evacuating time as compared with traditional combustion flashbulbs without an inner envelope. At the same time, due to the tolerancesin diameter of the tube glass, a considerable spreading in the fillingpressures of various lamps of the same manufacturing series will occur;the transporting path which is narrow as it is, is by no means constantover a series of lamps. This necessarily results in a series of lampsthe ignition times and light efficiencies, of which are by no meansconstant. Secondly, an inner envelope is used which should have a ratherthick glass wall so as not to break during firing the lamp. As anexample may be mentioned a wall thickness of approximately 1.4 mm. Itwill be obvious that just for minature flash bulbs a choice of aproportionally thick-walled inner envelope adversely influences theavailable effective lamp contents. While maintaining the external lampdimensions, such a lamp will show a smaller luminous efficiency with thesame choice of oxidizable metal, ignition mechanism, material of theouter envelope. A further drawback of the known combustion flash bulb isthat the shock wave which is formed during the ignition and combustionof the oxidizable metal and which propagates in the inner envelope willproduce large pressure differences between the space inside and outsidethe inner envelope. The inner envelope which is forced against the lampbase by spring action will then suddenly be lifted as a result of whichsaid shock wave will reach the space around the inner envelope shockwiseso that there is a possibility of explosion of the outer envelope.

It is the object of the present invention to mitigate the abovedrawbacks by providing a combustion flash bulb according to theabove-described type which is characterized in that the inner envelope,at its narrowed and remote from the lamp base, comprises an aperture thecross-section of which calculated at right angles to the longitudinalaxis of the lamp is at most 30 percent of the surface bounded by theinner wall of the inner envelope. By using an inner envelope having theabove aperture at the narrowed end remote from the lamp base it isachieved that on the one hand the evacuation and filling path during themanufacture of the lamp is considerably reduced with all the advantagesinvolved, and on the other hand the abovementioned shock wave canpropagate, via said aperture, in the space outside the inner envelopeand will hence be strongly attenuated. As a result of this an innerenvelope can be chosen to consist of a proportionally thin-walledmaterial (wall thickness, for example, 0.25 mm) which need no longerconsist of hard glass. lt even does not matter when the inner envelopeis destroyed during the combustion of the oxidizable metal. As amaterial for the inner envelope may be chosen, for example, the ratherreadily workable lime glass.

The dimension of the said aperture is chosen to be so that no red-hotparticles of the ignition mass occurring in the ignition mechanism canemerge through said aperture and reach the normally weaker top part ofthe outer envelope. On the other hand, said aperture should be chosen tobe so that the oxidizable metal which may be in the form of very narrowstrips of zirconium-containing material, does not emerge through saidaperture to in the exhaust tube at the lamp top during the manufactureof the lamp.

By choosing said inner envelope to consist of a thinwalled tubularmaterial, a larger filling of said envelope can be obtained, forexample, while maintaining the internal dimensions of the outerenvelope.

According to an embodiment of the flash bulb according to the invention,in which the length is at least 3 times the inner diameter and in whichthe ignition mechanism is near the lamp base, the inner envelope ismovable in the outer envelope in the axial direction, the ignitionmechanism being surrounded by the inner envelope in the two extremeaxial positions of the inner envelope. It is just in this type of slimflash bulbs that the evacuating and filling path, respectively, for theoxygen-containing gas is very long; the above-mentioned drawbacks thenbecome particularly prominent. It has been found that the inner envelopeshould remain slightly movable in the outer envelope but in such mannerthat the tubular inner envelope always surrounds the ignition paste orthe like, which forms part of the ignition mechanism. In particular, thedistance between the side walls of the inner envelope and the outerenvelope should preferably be chosen to be as small as possible.

According to another embodiment, the oxidizable metal accommodated inthe inner envelope is kept spaced apart from the ignition mechanism byan adhesive. A few drops of water glass have proved to be a reasonablesolution.

When according to a final embodiment of the lamp according to theinvention an inner envelope is'manufactured from a blue-colored vitreousmass, the outer blue layer of laquer which is usually provided on theouter envelope may even byomitted.

The invention may be applied to various types of combustion flash bulbs.It may be used for lamps which are operated with a low voltage source orwith a high voltage source by means of a piezo-electric ignition.

In order that the invention may be readily carried into effect, oneembodiment thereof will now be described briefly with reference to thedrawing.

The drawing shows a combustion flash bulb which comprises a tubularouter envelope 1, a lamp base 2 and a tip 3 which is obtained by sealingan exhaust tube 4. Two current conductors 5 and 6 are sealed in the lampbase 2 and terminate in a cup-shape cavity 7 which is present in araised base portion 8. An ignition The dimensions of the lamp are: outerdiameter 6 mm,

inner diameter 5 mm, height 24 mm.

The ignition of said lamp takes place by the shortlasting application ofa high voltage from a piezoelectric voltage source, as a result of whichbreak-down by the ignition mass occurs succeeded by a current passage inwhich the thermal energy necessary for starting the explosive combustionis produced in the ignition mass 9. For this type of ignition referenceis made to the Dutch published Pat. application No. 6,613,815.

A tubular inner envelope ll of thin-walled material (wall thickness 0.3mm) is arranged with some amount of play in the envelope 1 (a at most0.5 mm). This inner envelope 1] manufactured from lime glass is arrangedin the outer envelope so as to be slightly movable and that in suchmanner that said inner envelope always surrounds the ignition mass 9 inits two extreme axially moved positions. This inner tube intercepts thethrown-away red-hot particles during the ignition of the ignition mass 9which particles, in the absence of said envelope 11, would be thrownagainst the outer en velope and might give rise there to a considerableweakening and even fracture of the envelope 1. So the envelope 1] may beconsidered as a particle shield.

At its end remote from the lamp base 2, the inner envelope 11 comprisesan aperture 12 the diameter of which is 1 mm.

This aperture 12 is a contribution that in spite of the presence of theenvelope 11 on the one hand the lamp vessel 1 can easily be evacuated inall places of its contents and be filled with an oxygen-containingatmosphere. Furthermore, upon ignition of the lamp and the combustion ofthe metal wool 10, the shock wave moving in the longitudinal directionof the envelope 11 will be guided through said aperture 12 to the spacebetween the envelopes l and 11 as a result of which said shock wave isattenuated.

Furthermore, during the manufacture of the lamp the dome-shaped end ofthe inner envelope 1 1 with its aperture 12 holds the metal wool 10 at adistance from the exhaust tube 4.

The oxidizable metal 10 is furthermore kept spaced apart from theignition mechanism by a suitable adhesive. This may consist of a fewdrops of water glass which are deposited in the wide part of the innertube which is held with its aperture 12 downwards and in which a clew ofmetal wool is pressed.

If desirable, the inner envelope 11 may be formed from a blue-coloredvitreous mass.

What is claimed is:

l. A combustion flash bulb which comprises a hermetically sealedlight-pervious outer envelope and a tubular inner envelope which is openat its end facing the lamp base, the space in the inner envelopecommunicating with the space in the outer envelope, a filling of anoxidizable metal and an ignition mechanism being present in the innerenvelope, an oxygen-containing atmosphere prevailing inside the outerenvelope, wherein the inner envelope, at its narrowed end remote fromthe lamp base, includes an aperture the cross-section of whichcalculated at right angles to the longitudinal axis of the lamp, is atmost 30 percent of the surface bounded by the inner wall of the innerenvelope.

2. A combustion flash bulb as claimed in claim 1 of which the length isat least 3 times the inside diameter and in which the ignition mechanismis present near the lamp base, wherein the inner envelope is movable inthe outer envelope in the axial direction, the ignition mechanism beingsurrounded by the inner envelope in the two extreme axial positions ofthe inner envelope.

3. A combustion flash bulb as claimed in claim 2, wherein the clearancebetween the side walls facing each other of the inner envelope and theouter envelope is at most 0.5 mm.

4. A combustion flash bulb as claimed in claim 1, wherein the oxidizablemetal present in the inner envelope is kept spaced apart fromtheignition mechanism present near the lamp base by a suitable adhesive.

5. A combustion flash bulb as claimed in claim 1, wherein the innerenvelope is manufactured from a blue-colored vitreous mass.

1. A combustion flash bulb which comprises a hermetically sealedlight-pervious outer envelope and a tubular inner envelope which is openat its end facing the lamp base, the space in the inner envelopecommunicating with the space in the outer envelope, a filling of anoxidizable metal and an ignition mechanism being present in the innerenvelope, an oxygen-containing atmosphere prevailing inside the outerenvelope, wherein the inner envelope, at its narrowed end remote fromthe lamp base, includes an aperture the cross-section of whichcalculated at right angles to the longitudinal axis of the lamp, is atmost 30 percent of the surface bounded by the inner wall of the innerenvelope.
 2. A combustion flash bulb as claimed in claim 1 of which thelength is at least 3 times the inside diameter and in which the ignitionmechanism is present near the lamp base, wherein the inner envelope ismovable in the outer envelope in the axial direction, the ignitionmechanism being surrounded by the inner envelope in the two extremeaxial positions of the inner envelope.
 3. A combustion flash bulb asclaimed in claim 2, wherein the clearance between the side walls facingeach other of the inner envelope and the outer envelope is at most 0.5mm.
 4. A combustion flash bulb as claimed in claim 1, wherein theoxidizable metal present in the inner envelope is kept spaced apart fromthe ignition mechanism present near the lamp base by a suitableadhesive.
 5. A combustion flash bulb as claimed in claim 1, wherein theinner envelope is manufactured from a blue-colored vitreous mass.